Recent developments in the aerosol dispenser art have been along the lines of providing a dispenser in which the fluent product is dispensed by means of compressed air, rather than by one of the conventional propellants, such as Freon or the like. The toxic properties of Freon have been a subject of concern, and the development of compressed air type dispensers avoids the use of Freon, thus avoiding the problems associated therewith.
Recently developed dispensers which use a charge of compressed air to aspirate a product from a separate product container each time the dispenser is actuated are found in U.S. Pat. Nos. 3,672,545 and 3,733,010. However, these dispensers do not produce a spray with droplets of a size thought to be desirable for a medicament containing inhalent. Thus, in U.S. application Ser. No. 411,267, filed Oct. 31, 1973, now abandoned, in the name of Roger B. Caron et al, there is disclosed a dispenser in which fine droplets on the order of 1 to 10 microns can be generated in such a compressed air type dispenser by exerting a pressure on the product. Droplets of this size are thought to be most effective for an inhalent.
However, the apparatus of this lastmentioned application for generating the charge of compressed air and exerting a pressure on the product at the time of the release of the compressed air so as to dispense the product is somewhat complicated. Thus far, it has been the practice to exert this pressure on the product by means of mechanical actuation of a piston in contact with the product by a mechanical connection between the compressed air compressing means and the piston, or to exert a pressure on the product by means of the force exerted by the hand of the user of the dispenser directly on the product through the container for the product.
The type of dispenser in which pressure is exerted on the fluent product by means of a product pressurizing piston mechanically actuated by the compressed air means is somewhat complex in structure, requiring a number of parts and rather complicated shapes of parts, which are difficult to mold, such as in a material like plastic. The type of dispenser in which the pressure is exerted on the product by the force exerted by the hand of the user can be made in a somewhat less complicated manner, but again a number of parts are necessary, and the pressure is not always properly coordinated with the pressure exerted on the means for compressing the air.
Further, the structure of these devices does not lend itself readily to easily controlling the relative pressure of the compressed air charge relative to the pressurized product.
It is desirable to have such a device which has a simple construction, i.e. relatively few parts, and a structure which makes it possible to shape the parts in relatively simple shapes so that they are easily molded on conventional molding apparatus. It is further desirable to have such a structure in which the relative pressures of the compressed air and the pressurized product at the nozzle where they are mixed can be easily controlled by varying the structural features of the device. Technical progress in the art of such aerosol dispensers would be achieved if such a device could be provided.